This application claims the priority of International Application No. PCT/DE2010/000607, filed May 29, 2010, and German Patent Document No. 10 2009 024 117.5, filed Jun. 6, 2009, the disclosures of which are expressly incorporated by reference herein.
The present invention relates to the technical field of producing a hole in an object and in particular to producing a hole in an object by means of a beam for removing material.
Drilling by means of a material-removing energetic beam, such as, for example, an electron beam or laser beam drilling, has developed into a standard tool for many kinds of machining over the last few decades, for example for machining turbine blades or combustion chamber elements. These types of components may have a very high number of boreholes for example over 1,000. Beam drilling has proven to be an especially economical tool and is preferably used in particular in these applications because of the outstanding process efficiency.
Beam drilling is subject to physical limits, wherein particularly the so-called aspect ratio, i.e., the ratio between the borehole depth z and the borehole diameter d, determines the limits of the borehole geometry that may be fabricated in a manner that is stable for the process.
Various methods for carrying out these types of boreholes are known from the prior art. For example, dynamically adapting the laser focus length in laser drilling is known from U.S. Pat. No. 7,490,664. Furthermore, WO 2008/089292 shows adapting of the focus length in the case of deeper boreholes. U.S. Patent Application Publication 2004/0016730 shows carrying out an adaptation in order to focus a laser beam on a contact surface of a workpiece. Furthermore, U.S. Patent Application Publication 2003/0006220 shows continuously increasing a focus in a z direction in order to prevent damage to the substrate when layers of a substrate are being removed.
The object of the present invention is creating a concept that makes an improved execution of a production of a hole by means of beam drilling possible.
The present invention is based on the knowledge that a combination of a focus position repositioning, in which a bottom of a borehole is repeatedly placed in a focus position of the beam after a removal of material, and an additional change or modulation of a radiation characteristic of the beam, in which the bottom of a borehole is repeatedly placed in a focus position, makes it possible to produce a hole in a qualitatively higher-quality manner. In particular, it is thereby possible to produce high-quality and precise boreholes using laser beam or electron beam drilling even with a very high aspect ratio.
A method for producing a hole according to an exemplary embodiment comprises the generation of a beam for removing material such that a bottom of a borehole is placed in a focus position of the beam, and a removal of material by the impingement of the beam on the bottom of the borehole. To execute a focus position repositioning, a repeated placing of the bottom of the borehole in a focus position of the beam is carried out in order to compensate for the increased depth of the hole as a result of the removal of material. According to the invention, when the bottom of the borehole is repeatedly placed in a focus position, a radiation characteristic of the beam is changed. The changing of the radiation characteristic in this case may be a function of a momentary depth of the hole. In the case of exemplary embodiments of the present invention, the changing of the beam characteristic may include a predetermined changing or modulating of a beam caustic of the beam in such a way that with the repeated placement in a focus position, a degree of concavity of the beam caustic diminishes with an increasing depth of the hole. The change in the beam caustic with one exemplary embodiment includes a change in the focus diameter such that with increasing depth, the focus diameter becomes smaller. The modulation of the beam caustic may be accomplished by the changing of an aperture diameter, wherein the aperture diameter change may take place by introducing a selected aperture from a plurality of apertures in a beam path or by a change in the aperture diameter of a variable aperture.
With another exemplary embodiment, the change in the beam caustic may include a change in the focus diameter such that with increasing depth, the focus diameter becomes larger. In the case of one exemplary embodiment, the beam is expanded before passing through a focusing apparatus, wherein the modulation of the beam caustic includes a changing of a beam expansion. The advantage of this is a simple and cost-effective realization, wherein by a reduction in the beam expansion with an increasing depth of the hole, a depth of field (Rayleigh length) is increased, thereby enabling the beam shadowing at the borehole entrance to be reduced or completely eliminated. With one exemplary embodiment, a calculation of an optimal value for the beam expansion or an adaptive method is used to reduce the beam expansion only so much that the laser beam may be free of shadowing or largely free of shadowing in the borehole entrance. Correspondingly, with one exemplary embodiment in which an aperture diameter is changed, a calculation or an adaptive method is used to ensure that when the beam enters the hole there is no shadowing or only slight shadowing.
In one exemplary embodiment, a focus length of the beam, i.e., the distance of the focus point from the beam-generating drilling tool or focusing optics of the beam-generating drilling tool, is unchanged or substantially unchanged. This means that when the bottom of the borehole is repeatedly placed in a focus position, the adaptation to the depth of the borehole is achieved by a spatial change in the position of the object, while the drilling tool itself does not need to change its spatial position.
The beam for removing the material may be a laser beam or an electron beam in an exemplary embodiment.
Moreover, with one exemplary embodiment, the invention creates a device for producing a hole in an object wherein the device includes a radiation source for generating a beam for removing material and an apparatus for placing a bottom of borehole in a focus position of the beam. The apparatus for placing a bottom of borehole in a focus position in this case is set up such that after removing material on the bottom of a borehole, a repeated placing of a bottom of a borehole in a focus position is carried out. Furthermore, an apparatus for changing a radiation characteristic when the bottom of the borehole is repeatedly placed in a focus position is provided with the device. The device for changing the radiation characteristic in this case may be set up to carry out the change in the radiation characteristic as a function of a momentary depth of the hole. The apparatus for changing the radiation characteristic may furthermore be set up to modulate a beam caustic of the beam. In addition, an aperture device may be provided, wherein the aperture device is set up to change an aperture diameter when the bottom of the borehole is repeatedly placed in a focus position.
In the case of one exemplary embodiment, a device may have a focusing apparatus and an apparatus for expanding the beam before passing through the focusing apparatus, wherein the apparatus for changing the radiation characteristic is set up to change the beam expansion before passing through the focusing apparatus. The apparatus for changing the radiation characteristic maybe set up to reduce the expansion of the beam with increasing depth of the hole.
Furthermore, a controller may be provided for the radiation source in order to increase the energy density of a radiation on which the beam is based when the bottom of the borehole is repeatedly placed in a focus position. In particular, in the case of a drilling with beam pulses, the energy of a beam pulse is increased when the bottom of the borehole is repeatedly placed in a focus position, i.e., during focus position repositioning.
The device may be designed to modulate a beam caustic in such a way that there is no shadowing or no substantial shadowing when entering the hole.
The device may furthermore have an arithmetic unit for calculating a modulation of the beam caustic as a function of a momentary depth of the hole.
Furthermore, the device may be set up to carry out a spatial change in the position of the object when the bottom of the borehole is repeatedly placed in a focus position.
Moreover, the present invention creates a computer program with a program code for execution, if the computer program runs on a computer, a method for controlling a production of a hole by means of a beam for removing material in an object having the step of a control of a change in a radiation characteristic of the beam as a function of a momentary depth of a bottom of a borehole of the hole, when the bottom of the borehole is repeatedly placed in a focus position.
Preferred exemplary embodiments of the present invention will be explained in more detail in the following making reference to the enclosed drawings.